Re: My (first ) try with Jim Patterson Cuprotype-question
CUPROTYPE (Obernetter's Process, Ferrocupric Process, Copper Print) by Jim Patterson 10-5-2007 J. B. Obernetter developed his process in 1864. The original formula is noted in Jan Arnow's "Handbook of Alternative Photographic Processes", 1982, page 113. "Copper Print" is from a 1978 Popular Photography "How to" guide. See http://pinhole.stanford.edu/cp.htm for details. GENERAL: A contact printing photographic process analogous to Cyanotype; full size negative, print frame, UV exposure. The image is reddish-brown copper ferrocyanide. All solutions are w/v (weight in a final volume), dissolving each salt completely before the next is added, in 10% less water than the final volume. Make up to final volume when all salts are dissolved. Use very pure chemicals and distilled water, and plastic or glass trays, vessels, stirring rods, etc. Try these processes at your own risk. The chemicals can cause property damage, environmental damage, personal injury, or even death. Store the stable solutions in brown glass bottles, plastic caps, plastic cap liner (corrodes metal). Damp coated paper (high humidity) may damage negatives. Use kitchen plastic wrap between the negative and paper if needed. Sunlight and florescent light fog the coated paper. Agitate trays during processing. PATTERSON'S modified Obernetter's Process (MO3) SENSITIZER: 100 ml distilled water (Stable) 12grams ferric ammonium citrate (green)* 12 grams copper sulfate, hydrated (CuSO4.5 H2O) *ferric ammonium oxalate & ferric oxalate do not work; precipitate with copper. Light sensitive component; mix in safelight area (yellow bug light, tungsten) DEVELOPER: 1000 ml distilled water (stable) 10 grams citric acid (hydrous or anhydrous) 10 grams ammonium thiocyanate (NH4SCN) (can substitute potassium- or sodium- thiocyanate) Or make a 10% C.A, 10% A.T. stock solution and dilute 1 part stock : 9 parts water. CLEARING BATH: 750 ml distilled water + 250 ml DEVELOPER (1 part developer : 3 parts water) TONER: 1000 ml distilled water (Stable) 20 grams potassium ferricyanide (K3Fe(CN)6) (or make a 20% stock solution and mix1 part stock: 9 parts water) WASH: 900 ml tap water + 100 ml white vinegar, or add 5 ml glacial acetic acid (CAUTION: noxious fumes) to 955 ml water. If your tap water has iron, use distilled water to avoid blue staining. This is a 0.5 % acetic acid solution. Coat paper with sensitizer in a darkened room with yellow bug light or low wattage tungsten lights; no fluorescent or sunlight. Dry with forced air (fan, no heat) & expose in print frame to UV light until an image is present. Work out your own exposure time. I have kept coated (no dichromate) dry paper in a dark, dry place for 3 days and it works ok. I don't know how long it lasts. I usually coat, dry, and expose the same day. Adding a drop of Kodak Photoflo to the sensitizer makes it coat better. Tween 20 might work (I didn't have any) but I'm unsure if it's compatible with copper. Tray develop in DEVELOPER until the shadows clear of orange color and are pale gray. About 3-5 minutes. Highlights may have a slight orange stain at the end of development. The developer will be slightly orange in color (iron salts). One shot developer. Do not save or reuse. Place directly into CLEARING BATH, series of 3 tray or solution changes, until highlight are clear (paper white) and solution is clear. If you don't get all the orange out (iron salts) the print will be blue stained in next step. About 5 minutes, longer with thick or unsized papers. The image is now copper (I) thiocyanate, which is a dye mordant. (You can stop at this point and dye-tone the image with basic dyes (methylene blue, basic brown, basic fuchsin, etc) in a 2.5 % acetic acid dye bath (0.1% dye). Wash in a 2.5% acetic acid wash and dry. 2.5% acetic acid is 1 part vinegar : 1 part water.) Or continue on for the Cuprotype if you are not dye toning. Place directly into TONER until fully toned to reddish brown image (About 15-20 min). The image is now copper ferrocyanide.) A tray of toner can be used for more than one print but discard when it slows, and do not pour back into the stock bottle. The thiocyanate from the prints causes it to break down. Discard at the end of a work session. Transfer to WASH, 3 or more tray or solution changes until highlights are clear and solution is clear. Check the back of the paper. About 10 minutes. Thick papers clear slowly. Thin or dip sized papers clear faster. See TROUBLESHOOTING. If your tap water is alkaline or hard, final wash in distilled water + vinegar as above. Dry and marvel. CONTRAST CONTROL: Do NOT use potassium chlorate, as the copper chlorate that forms is EXPLOSIVE when dry!!! It may be better to tailor your negative to the characteristic curve with 1 drop dichromate to clear the highlights. I use 30% ammonium dichromate drops (CAUTION: dermatitis, carcinogenic; handle carefully), with 0-4 drops in 2 ml sensitizer. Ammonium persulfate and hydrogen peroxide do not work. (Just for your info, I tried potassium chlorate in a very safe area and it didn't work either.) PERMANENCE: USDA tests show that copper ferrocyanide used as a pigment in outdoor fences holds up well. Probably as permanent as Cyanotype, and does not bleach on light exposure. AMIDOL TONING: see the Copper Print http reference. Works fast. 250 ml water, 5 grams citric or acetic acid, 0.2 gram amidol. Soak the print for 1 minute, wash in the WASH and dry. It darkens dramatically to a dark warm brown as it dries. I think the copper ferrocyanide acts as a mordant, binding the amidol, which oxidizes to the familiar dark brown as it dries. GALLIC ACID TONING: Brown image, lower Dmax just as with Cyanotype. PAPER: I have used Crane's Diploma Parchment (very sharp image, no bleeding, & ferricyanide stain clears easily). Arches Hot Press Watercolor Paper (slight texture) and Cold Press (moderate texture) work but are slow to clear the ferricyanide stain. (See TROUBLESHOOTING) I am sure other papers work, but some do not. Don't use buffered paper or paper filled or sized with calcium carbonate or magnesium carbonate as alkalis bleach the image. Works on cotton fabric also. TROUBLESHOOTING: Low Dmax: double coat the paper, drying between coats or size the paper. Blue Staining: Iron contamination of solutions, iron not cleared completely in CLEARING BATH, or toner (ferricyanide) was not washed out of the print. Increase the clearing or wash times. If a thick paper has a yellow ferricyanide stain after a long wash, you can soak it in a solution of 500 ml water, 5 grams acetic acid, 5 grams zinc sulfate & 5 grams sodium sulfite, which converts the potassium ferricyanide to zinc ferrocyanide, a white pigment used in marine paints. Then WASH to remove excess salts and dry. ARCHIVAL WASH: Don't! The long alkaline tap water wash will dissolve part of the image making it fuzzy or weak. Use tray washes of dilute acetic acid. MOUNTING & STORING: Don't use buffered mats or papers. See PAPER above. EXPOSURE: I use a homemade UV unit of eight, 18-inch black light bulbs from Home Depot about 3 inches from the print frame. My exposure time is about 5 minutes with no dichromate added. 30-150% longer with increasing dichromate additions. COPPER PRINT: A printing out version. Develops in water. See the http reference. I get staining of highlights and bleeding of shadows, but Obernetter's gives sharp prints with clear highlights. EXPERIMENTAL NOTES: I tried the original Obernetter's formula: Sensitizer: ferric chloride, copper chloride, with added concentrated hydrochloric acid. Developer: potassium thiocyanate with added concentrated sulfuric acid and some senstizer added (why?). Slow process, very long scale and very difficult to clear the iron salts. Split tones with reddish brown shadows and blue highlights were common, due to cyanotype reaction in the toner when all ferric salts not removed in washing. Almost impossible to clear the iron with a water wash. The developer is dark blood red and can't see the print unless you pull it out of the solution. I don't recommend it. I first modified the formula (MO1) to use 1 % citric acid instead of hydrochloric acid and sulfuric acid in the sensitizer and developer respectively, and left the sensitizer out of the developer. The clearing bath I added to get the iron out and keep some thiocyanate ion in the bath to keep the copper (I) thiocyanate in the print by common ion effect. It is also slow (20 min exposure) but clears the iron out easily. Very fine grained smooth image. The 21 Stouffer step wedge gives about 18 steps. (OM2) I next tried ferric ammonium citrate to replace the ferric chloride with a great increase in speed and about the same long scale on step wedge. (OM3) is the process above, with ferric ammonium citrate and copper sulfate. If you have very long range negatives, such as an older process with glass negatives, the long range of the process without dichromate may match well. The best print is probably from a long range negative with 1 drop dichromate in the sensitizer to keep the highlights clear and the scale matching your negative. Photoshoping the image to match the scale of the process will probably work great. With very high dichromate levels the print is grainier and much longer exposure. The Copper Print is analogous to the New Chrysotype by Mike Ware, in that the potassium ferricyanide and copper sulfate are mixed together as the sensitizer and the process is mostly a printing out one with washing (developing) in water. But without ligands (complexing agents) like citrate, acetate, etc., the copper precipitates as copper (II) ferricyanide, just as gold does in chrysotype without the 3,3 dithiopropionic acid ligand. I tried disodium EDTA alone, sodium citrate (tribasic) alone, ammonium citrate (tribasic) alone and combinations with sodium acetate as in the reference. The starting weight ratio of copper sulfate, hydrated, to sodium citrate is 1:4 which is also about the molar ratio. Speed is fast, but staining of highlights and bleeding is a problem, just as with the New Chrysotype with low ligand ratios. By increasing the ratio to 1:5 and 1:6 the staining of highlights is reduced and the contrast is increased, but the Dmax is decreased and exposure is increased, just as with the New Chrysotype. Also, as with New Chrysotype, the Copper Print sensitizer is unstable after mixed and must be coated, exposed and washed (developed) quickly. I never got prints as sharp and clean with this process as with the modified Obernetter's. I also had great difficulty with ammonium persulfate causing a precipitate (potassium persulfate was worse.) Ammonium dichromate worked better for me. I also coated paper with ferric oxalate 10 % solution and exposed. Very fast exposure. (1 min.) This can then be placed in TONER directly for a cyanotype, or transposed to copper ferrocyanide by using a reagent of copper sulfate, complexed with citrate (1:5 sodium citrate) and ammonium thiocyanate The reagent is unstable after mixing and must be kept in separate bottles and mixed just before use. It is slow to convert to copper (I) thiocyanate, and then it is cleared and toned just as for Obernetter's. The image tends to be grainy. Obernetter's has stable reagents and is faster to complete. The image is redder, grainier, & printing speed faster with increasing pH of the sensitizer used. I like the color of the modified Obernetter's detailed above. Lower pH sensitizers respond to smaller doses of dichromate. Higher pH sensitizers take a lot of dichromate to modify contrast. GOOD SOUPING! I know you real photographers can make great images with these processes. ----- Original Message ----- From: "Robert W. Schramm" <schrammrus@hotmail.com> To: <alt-photo-process-l@usask.ca> Sent: Wednesday, October 31, 2007 7:38 PM Subject: RE: My (first ) try with Jim Patterson Cuprotype-question Christina, Tried to google and tried Alt-process-archives but could not find. Could you please repost info on cuprotype. I would much appreciate. Many thanks. Bob Schramm Check out my web page at: http://www.SchrammStudio.comDate: Tue, 30 Oct 2007 21:02:52 -0600
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